In signal processing, a differential circuit that deals with a differential signal is often used. Compared to a single phase signal, a differential signal is less likely to be influenced by, for example, a noise (an in-phase noise), or allows a signal range to be widened twice. Therefore, a differential circuit is often used in a case of, for example, dealing with an analog signal having relatively small amplitude.
In a case that a single phase signal is supplied to such a differential circuit, it is necessary that a single phase differential conversion circuit is provided for converting the single phase signal to a differential signal and supplying the converted signal to the differential circuit. For example, in Patent Literature 1, disclosed is a balun circuit (a single phase differential conversion circuit) having a differential pair configured of two field effect transistors (FETs).
Also in a communication device, a high frequency switch (an RF switch) is often used in selecting, as an operation object, one circuit from a plurality of circuits or in selecting, as a processing object, one signal from a plurality of signals. Specifically, for example, in a wireless communication device having a transmission circuit and a reception circuit, a high frequency switch is used to connect an antenna with the transmission circuit in signal transmission, and to connect the antenna with the reception circuit in signal reception. Moreover, for example, in a reception circuit having a plurality of attenuators, a high frequency switch is used to switch the attenuators according to signal intensity.
As to such a high frequency switch, various technologies have been disclosed. For example, in Patent Literatures 2 to 4, disclosed is a high frequency switch that includes a switching transistor and a resistor connected to a gate of the switching transistor, and is configured to apply a control voltage to the switching transistor through the resistor.